Although by pretty much all measures (extension, growth, alk/ca uptake, etc) my tank inhabitants have been thriving, over the last 2-3 months, I've had a lot of brown/green algae growing primarily on my sand. It never used to happen, in fact my larger chunks of rubble in the sand were turning purple with coralline growth while the rest was largely staying white. My nutrients are as low as they've ever been - NO3 = ~3-4ppm and PO4 = .04ppm and have been stable for quite some time. The one thing I noticed a few weeks ago is my DI resin must have been exhausted and I was reading 1 TDS coming out of the RO filter so I changed the resin. Just for fun, I took a sample of my recently mixed salt water before I changed the resin and sent it off to Triton for an ICP test to see if there was something coming through that could explain and in looking at the results only one thing jumps out at me, Iron. I'm using tropic marin pro salt, curious if anyone knows if this is normal, or if I have some other source. Additionally curious if any hypothesis if this could be contributing to my algae issue?